1. Field of the Invention
The present invention relates to methods of machining wheel bearing caps or other bearing caps in a CNC work center.
2. Background Art
Bearing caps are used to secure a bearing that journals a shaft. Bearing caps are used in vehicles to retain axle shafts within an axle and wheel bearings for a wheel assembly. Bearing caps may also be provided to retain crankshaft bearings on an engine and may also be used in other types of machinery. Bearing caps generally have a semi-circular body portion and flanges for receiving bolts that are used to secure the bearing cap to a supporting member or second part of a bearing retaining assembly. Bearing caps must be machined to close tolerances to avoid assembly problems and excessive scrap and salvage expense.
Bearing caps may be formed in a casting operation in which tolerances are typically required to be held to ±0.030 inches for castings having a distance between measured points of between 0 and 3 inches and ±0.045 between 3 and 8 inches. Castings are normally formed with a draft angle that is required to remove the casting from the casting mold. The unusual shape of a bearing cap makes it difficult to properly fixture one or more bearing caps as they are machined.
Bearing caps normally must be machined after casting to provide uniformity from part to part. For example, at one machining center location, a bearing cap may be fixtured while bolt holes are drilled and counterbored on the fastener shoulders of the bearing cap with the end faces of the bearing cap being milled to a tolerance of ±0.010 inches.
The relatively broad tolerance for a cast bearing cap is three times the tolerance allowed for machining surfaces which makes it difficult to fixture cast bearing caps for initial machining operations. After initial machining operations are performed on the bearing cap, accurately machined surfaces are available to locate the bearing cap for subsequent machining operations.
There is a need for a method of machining a plurality of bearing caps simultaneously at a work center that allows the bolt hole locations and machined surfaces to be accurately located. The above problems and needs are addressed by Applicant's invention as summarized below.